Through lack of skill or by accident, most driver will occasionally
scuff their tires against a concrete curb. For ex. through poor parking
skills or by having to squeeze past other cars along a very narrow
road.

How much rubbing damage (scratches, scuffs, etc) is permissible to the
sidewall of a tire before it would have to be replaced? Or is minor
scuffing to be considered part of 'normal wear & tear'?